Digital radiography (DR) is an advanced imaging technology, which combines the computer digital image processing and the X-ray emission technology. According to its advantages of low radiation doses, high image quality, high detection rate, and high accuracy, digital radiography has been widely used in many fields, such as aerospace, security, healthcare, etc. In medical digital radiography, X-ray signal is generated by a generator, and radiated to an imaging target such as a human body or other subjects. Then the X-ray signal can be detected by an X-ray detector, such as a flat panel detector. After a series of processes, an image of the radiated area can be formed, which may be used in disease diagnosis, medical research and other aspects.